When installing OC 3.0 on a fresh computer-setup with e.i. LinuxMint 20.xx you can encounter some unclear errors (at least I did). So what do you have to check whether the required software is already is installed. If not... install it

First MySql:
- MySql-server 8.0
- MySQL-server-core 8.0 (both come together)
- MySQL-client 8.0
- MySQL-client-core 8.0 (both come together asl well)
PHP-related:
- PHP 7.4
- PHP 7.4-cli
- PHP 7.4-curl
- PHP 7.4-gd
- PHP 7.4-json
- PHP 7.4-mysql
- PHP 7.4-opcache
- PHP 7.4-readline
- PHP 7.4-xml
- PHP 7.4-zip
In previous versions it all came along with one initial PHP setup but with the last versions it has changed. So it can save you a lot of time when you check this.
Have fun.